fix warning of root metro config (#27883)
fix warning of root metro config (#27883)

Summary:
fix https://github.com/facebook/react-native/issues/27620

## Changelog

[Internal] [Fixed] - Fix warning of packager
Pull Request resolved: https://github.com/facebook/react-native/pull/27883

Test Plan: - run `./scripts/packager.sh` and no warning displayed

Differential Revision: D19619571

Pulled By: cpojer

fbshipit-source-id: 3cd6383d9b0f7e133a9253b19ad626fcc93d5bed

myntra/react-native,exponent/react-native,janicduplessis/react-native,hammerandchisel/react-native,exponentjs/react-native,facebook/react-native,facebook/react-native,exponentjs/react-native,exponent/react-native,hammerandchisel/react-native,janicduplessis/react-native,exponentjs/react-native,exponent/react-native,pandiaraj44/react-native,javache/react-native,myntra/react-native,myntra/react-native,hoangpham95/react-native,facebook/react-native,hoangpham95/react-native,facebook/react-native,pandiaraj44/react-native,hoangpham95/react-native,janicduplessis/react-native,facebook/react-native,exponentjs/react-native,javache/react-native,javache/react-native,janicduplessis/react-native,janicduplessis/react-native,myntra/react-native,hammerandchisel/react-native,facebook/react-native,hoangpham95/react-native,myntra/react-native,arthuralee/react-native,hoangpham95/react-native,exponentjs/react-native,janicduplessis/react-native,myntra/react-native,javache/react-native,arthuralee/react-native,hoangpham95/react-native,hoangpham95/react-native,javache/react-native,pandiaraj44/react-native,exponent/react-native,pandiaraj44/react-native,janicduplessis/react-native,hoangpham95/react-native,facebook/react-native,exponent/react-native,pandiaraj44/react-native,javache/react-native,arthuralee/react-native,janicduplessis/react-native,hammerandchisel/react-native,javache/react-native,exponent/react-native,myntra/react-native,javache/react-native,exponentjs/react-native,javache/react-native,hammerandchisel/react-native,facebook/react-native,arthuralee/react-native,hammerandchisel/react-native,exponentjs/react-native,pandiaraj44/react-native,facebook/react-native,exponentjs/react-native,pandiaraj44/react-native,arthuralee/react-native,hammerandchisel/react-native,hammerandchisel/react-native,myntra/react-native,pandiaraj44/react-native,exponent/react-native,myntra/react-native,exponent/react-native